Europium and manganese activated strontium chlorosilicate phosphor

ABSTRACT

A STRONTIUM CHLOROSILICATE PHOSPHOR, SR5SI4CL6O10 ACTIVATED BY EUROPIUM AND MANGANESE IS DESCRIBED. THE PHOSPHOR PRODUCES A BRIGHT GREEN EMISSION WHEN EXCITED BY 2537 AND 3650 ANGSTROM RADIATION.

United States Patent 3,790,490 EUROPIUM AND MANGANESE ACTIVATED STRONTIUM CHLOROSILICATE PHOSPHOR Ranajit K Datta, East Cleveland, and Thomas W. Luscher, Wickliife, Ohio, assignors to General Electric Company Filed Mar. 3, 1971, Ser. No. 120,511 Int. Cl. C09k N54 US. Cl. 252301.4 F 1 Claim ABSTRACT OF THE DISCLOSURE A strontium chlorosilicate phosphor, Sr Si Cl O activated by europium and manganese is described. The phosphor produces a bright green emission when excited by 2537 and 3650 Angstrom radiation.

BACKGROUND OF THE INVENTION The instant invention relates to color-corrected highpressure mercury vapor lamps and phosphors therefor.

The are in a high-pressure mercury vapor lamp (HPMV) produces lines of varying energy in the ultraviolet, blue and yellow portions of the spectrum. Major radiation occurs at 405, 436, 546 and 578 nanometer (nm.) in the visible spectrum, and also at 253, 296 and 365 in the ultraviolet. Because of the lack of radiation in the green (about 500 nm.) and especially red (about 600 nm.) portion of the color spectrum, the high-pressure mercury lamp emits a bluish light. The absence of red and green radiation causes most colored objects to appear distorted in color values. The ideal would be a lamp having a continuous spectrum and appropriate energy distribution covering the entire visible region.

Mercury vapor lamps are good emitters of ultraviolet radiation, especially with wavelength at 3650 A. The red deficiency and color rendition of HPMV lamps are much improved by coating the inside of the outer envelope with a red-emitting phosphor excited by the ultraviolet energy generated by the mercury arc. The red phosphors commonly used in HPMV lamps are tin (stannous Sn activated strontium orthophosphate (US. Pat. 3,110,680, Koelmans et al., June 1957), and manganese-activated magnesium fluorogermanate (US. Pat. 2,748,303, Thorington, May 1956). More recently, europium (Eu activated yttrium vanadate and europium (Eu )-activated yttrium vanadate phosphate Ref.: T. W. Luscher and R. K. Datta, Illuminating Engineering vol. 65, No. 1, January 1970, pp. 49-53) have found extensive use in high-pressure mercury vapor lamps. These phosphors emit in the red portion (about 600-650 nm.) of the color spectrum, thus producing a color-corrected mercury discharge lamp. However, the absence of green in the spectrum still remains and greenish objects appear distorted in color values under color-corrected HPMV lamps coated with red-emitting phosphors only.

SUMMARY OF THE INVENTION According to the present invention Mn -doped Euactivated strontium chlorosilicate (Sr Si Cl O :Eu) can be mixed with phosphor emitting in the red only and the blend when applied as a coating on the inner surface of the outer envelope of the lamp produces a higher color temperature lamp with better color rendition in the center portion of the visible spectrum.

We have confirmed that the phosphor Bu -activated Sr-chlorosilicate (Sr Si Cl O :Eu responds well to both 2537 and 3650 A. radiation and has a broad emission band extending from 400 to 650 nm., peaking at 490 nm. Optimum luminescence brightness is obtained at 1:0% by wt. of europium. Going further, according to the present invention, we have discovered that when Euactivated Sr-chlorosilicate (Sr Si Cl O :Eu is doped 3,790,490 Patented Feb. 5, 1974 with manganese (Mn the brightness under 2537 and 3650 A. is enhanced without any significant change in the emission spectrum.

DESCRIPTION OF DRAWING In the drawings:

FIG. 1 is a graph of the effect of temperature on the luminescence of strontium chlorosilicate under 2537 A. excitation.

FIG. 2 is a similar graph under 3650 A. excitation.

FIG. 3 shows a high pressure mercury vapor discharge lamp containing a phosphor coating in accordance with our invention.

DETAILED DESCRIPTION Compositions and luminescent data for Sr5Si4ClnOm: Eu, Mn

Percent relative Eu Mn conc., cone, Brightness, Brightness,

Composltion percent. percent 2537 A. 3650 A.

Sr5Si4C1aO1o 1 0 100 100 Sr5Si4CltO1o- 1 0. 25 105. 5 109. 0 Sl5Si CleO 1n. 1 0. 5 107. 5 115. 0 S15Si4CluO10-- 1 1. 0 108. 5 117. 0 SlsSirCltOw 1 1. 5 107. 0 108. O 5Si4C16010- 1 2. 0 93. 0 100 SIsShCloOm- 1 2. 5 97. 5 102 Sr5Si4CluO1o. 1 3. 0 93. 0 107 The eifect of manganese doping on strontium chlorosilicate is an enhancement of the effect of the europium activation and we have found it to hold throughout the beneficial range of europium doping extending from about 0.01 to 3.0% by weight.

According to another aspect of our invention, we have observed that a mercury lamp coated with a blend of europium (Eu +)-activated green-emitting strontium chlorosilicate (with or without manganese doping) and a characteristically red-emitting phosphor will produce an excellent color rendition with optimum brightness and commercially acceptable maintenance. To be suitable for application in high pressure mercury vapor lamps, a phosphor should be responsive to the main emission lines (especially to 3650 A. radiation) of the discharge and its luminescence, that is the nature of the spectrum and its intensity, should not be substantially adversely affected by high operating temperatures. This is because the outer envelopes of mercury lamps operate in the temperature range of 200 to 400 C. We have studied the effect of temperature on Eu +-activated strontium chlorosilicate and found that the phosphor has very good temperature maintenance. FIGS. 1 and 2 show the effect of temperature on the luminescence brightness of Sr Si Cl O :Eu under 2537 and 3650 A. excitations, respectively. At 300 C. the luminescent brightness under 2537 and 3650 A. excitation are about and 55%, respectively of the room temperature brightness. With manganese doping, the high-temperature brightness improves even further. Thus, with about 1% manganese doping the luminescence brightnesses at 300 C. under 2537 and 3650 A. excitations are about and 63%, respectively, of the room temperature brightness. Such good high-temperature brightness data, according to the present invention, makes these two phosphors (Eu +-activated strontium chloro- DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, there is shown a high pres- The maintenance figure is the percentage of lumens measured at 4000 hours of life to lumens measured at 100 hours, and it is higher with the blend. The color temperature is rising with increasing proportion of strontium chlorosilicate in the blend but it is an increase due to the Sure mercury Vapor p 1 comprising q arc tube presence of green and not merely an excess of blue. The 2 en s d Within a Vitreous Outer jacket envelope 3 color ranking is based on visual observation. Rank 1 is provided with a screw base 4. The are tube is pr vi d lacking in the middle range of the visible spectrum. Rank with main ec r d s 6 at each e and an au y 2 has improved response. Rank 3 has the best color rendi electrode 7 located adjacent main electrode 5. The are tion with both reds and greens appearing natural, Rank tube contains a measured amount of mercury which is 1 i weighted t h w rd green and is lacking i completely vap during Operation a d a inert ta red and while its color temperature is higher, it repreing gas such as argon as is conventional in the arc. sents a departure from the black body locus. In blends The are tube iS supported within the outer jacket by useful for high pressure mergury va or lamps, the pera frame or p comprising a Single Side rod 8 and metal centage by weight of strontium chlorosilicate extends straps 9. The frame also serves as a conductor between f 5% to 50% by weight where th th component electrode 6 and the base shell. Another C ndu tor 10 C of the blend is a characteristically red-emitting phosphor nects the other electrode 5 to the center contact of the f i il ti l i b t h ific Percentage ill base. Starting electrode 7 is connected to main electrode b governed b choice f di i h h d i 6 at the opposite end of the arc tube by a current limit- 90 tended application of the lamp. The preferred percentage ing resistor 11 is conventional fashion. of strontium chlorosilicate in a blend with YV,PO for A coating 12 Of a P p blend in accordance With general lighting lamps is from to 30%. Depending ur i v namely divalent europium 1 v upon the nature of the characteristically red-emitting strontium chloros cate e t g in h green t another phosphor selected for the blend, the proportion of stron- P P emlttmg characteristically m the red is coated tium chlorosilicate in the blend and other factors such as 9 the Inner slfrface of the B envelope or the thickness of the coating, the use of a blend according Jacket 3 accordmg to CQHVCHHOPM techmques', to our invention permits the design of high pressure mer- BY Way of examples luustmnng the propqmes of our cury vapor lamps having color temperatures ranging from improved phosphor and phosphor blends, high pressure about K to 50 0 K mercury vapor lamps as described above were coated with Wh t 1 d d t b L yttrium vanadate phosphate activated by europium and a We 6 as new eslre 0 Secure y etters blends of yttrium vanadate phosphate activated by euro- Patent of the t States,1s: pium with approximately 20% 25% and 40% by Weight 1. green emitt ng S r S| Cl O phosphor coactivated of strontium chlorosilicate (Eu activated, Mn doped). Wlth dlvalent ellmpmm m a concentramfn f The various phosphors were prepared as suspensions of to 9 by Welghi and dlvalent manganese lon 1n a conthe same particle size, mixed together, and applied con centratton from 0.01 to 3. y Welght 80 as to Improve ventionally. The following table gives lamp data using phosphor brightness without significantly changing the the blends. emission spectrum under ultraviolet excitation.

TABLE II Mainte- Percent naneo, Color Color Phosphor LP red percentL temp.,K rank YV,PO4 53.0 as 89.5 3,880 1 W, P04 20% srtshohom. 54. 4 7. 6 96. a 3,960 2 W, P04 25% SnSisClsOm.-- 53. a 7. 5 05. 9 4,220 a YV, P04 SI'5Si4C16010 53. 0 5. 9 95. 5 4,500 la References Cited UNITED STATES PATENTS 3,513,103 5/1970 Shafier 25231.0 P 3,516,940 6/ 1970 Lagos 25230l.4 P

FOREIGN PATENTS 1,087,655 10/1967 Great Britain 252-30l.4 F

OSCAR R. VERTIZ, Primary Examiner I COOPER, Assistant Examiner US. Cl. X.R. 

